Gases including a harmful and combustible gas, such as silane gas (SiH4) or halogen-based gas (NF3, ClF3, SF6, CHF3, C2F6, CF4), are discharged from a semiconductor manufacturing apparatus. Such an exhaust gas (processing gas) cannot be emitted into the atmosphere as it is. Therefore, the exhaust gas is generally introduced into an abatement apparatus where the exhaust gas is made harmless by oxidation through combustion. As this treatment method, a combustion-type exhaust gas treatment apparatus in which a fuel gas is used to form a flame in a furnace and to perform exhaust gas treatment therein is widely used.
In a combustion-type exhaust gas treatment apparatus for use in a semiconductor industry and a liquid crystal industry, a fuel and an oxidizing gas (oxygen-containing gas) are mixed to combust the fuel and to form a flame, and a processing gas is mixed with the flame to perform gas treatment. Therefore, a large amount of dust (mainly SiO2) and a large amount of an acid gas as by-products of combustion treatment of the exhaust gas are expected to be generated. As a conventional combustion oxidation method, a method in which LNG and pure oxygen are used to form a pure-oxygen flame having a high temperature and a processing gas is heated by the high-temperature pure-oxygen flame to be decomposed is known. However, this method is problematic in that nitrogen contained in the exhaust gas is decomposed by the high-temperature flame resulting from the attributes of pure-oxygen combustion, thereby generating a large amount of nitrogen oxide (NOx) additionally.
Further, there has been also known a method for forming a flame by air without using pure oxygen, and heating a processing gas at a relatively low-temperature by mixing the processing gas with the flame. In this case, generation of nitrogen oxide (NOx) is suppressed, but decomposition performance of a persistent gas such as PFCs requiring a high-temperature flame is lowered. Further, this method has a problem of generating CO because the flame has a low temperature.
Further, in the combustion-type exhaust gas treatment apparatus, it is necessary to perform regular maintenance for removing powdery product attached to and deposited on an inner wall surface of a combustion chamber. Therefore, an additional mechanism, such as a scraper, is required to regularly scrape off the powdery product attached to and deposited on the inner wall surface of the combustion chamber.
Patent document 1 discloses a combustion-type exhaust gas treatment apparatus which does not necessitate a mechanism such as a scraper for scraping off powdery product. In the combustion-type exhaust gas treatment apparatus disclosed in patent document 1, a combustion treatment unit of an exhaust gas as an object to be treated comprises an exhaust gas treatment combustor (burner) for forming a flame therein, a cylindrical body provided below the exhaust gas treatment combustor, a water reservoir provided between the exhaust gas treatment combustor and the cylindrical body, and a water-film formation mechanism for forming a water film on an inner wall surface of the cylindrical body. In the combustion treatment unit, a flame is formed in the combustor, combustion treatment (heating treatment) of the exhaust gas is performed in a combustion treatment chamber, inside the cylindrical body, disposed at the downstream side of the flame, and a swirling flow of water is formed in the water reservoir to form a spiral water film on the inner wall surface of the cylindrical body. According to this patent document 1, the following description is made: Because the water film is formed on the inner wall surface of the cylindrical body, heat insulation is performed by the water film, and an inexpensive material such as stainless steel can be used for the cylindrical body. Further, the water film can wash away the powdery product to prevent the powdery product from adhering to the inner wall surface of the cylindrical body. Furthermore, the water film can wash away a corrosive gas to prevent the inner wall surface of the cylindrical body from being damaged.